Drawing a Spark from Darkness John Walsh and Electric Fish by Marco Piccolino and Marco Bresadola
This article will also appear in Trends in Neuroscience.
Posted December 7, 2001 · Issue 116

Abstract

John Walsh's research on electric fish, carried out between 1772 and 1775, proved fundamental for demonstrating that electricity might be involved in animal physiology and, moreover, in favoring a period of great progress in both the physiology and physics of electrical phenomena. However, Walsh is hardly known to modern neuroscientists and is largely neglected by science historians also. One of the reasons for this neglect is that he never published his "crucial experiment," that is, the production of a spark from a discharge of the electric eel.

It is with pleasure that I inform you that they have given me an electric spark, perceptible in its passage through a small gap or separation made in a tin lamina pasted on a glass. These fishes were in the air; since this experience has not succeeded in water; their electricity is very much stronger than that of the Torpedo, and there are some considerable differences in their electrical effects.

These few lines, printed in 1776 in an important scientific journal published in Paris by Abbé François Rozier [1], are of great historical relevance, because they report the first successful attempt to obtain a visible spark from an electric fish, the eel of Surinam or Gymnotus (figure 1). The results of the experiment were never published by the researcher, John Walsh (1726-1795), fellow of the Royal Society and member of the English Parliament. Walsh, however, wrote to Jean-Baptiste Le Roy, who transcribed these lines in a correspondence published in Rozier's journal. The passage reported represents an "abstract" of an experiment never to be published in extenso.

Walsh demonstrated the eel's spark experiment to colleagues and visitors in his London house in the summer of 1775 (and on later occasions). This peculiar way of publicizing scientific results (which often preceded the written report) depended, in part, on the necessity to have numerous and authoritative witnesses of scientific results, in the absence of other direct objective ways of documenting them. It was particularly necessary for a result that had been sought after unsuccessfully for so long. The production of a spark from the discharge of an electric fish was an event open to incredulity, because the idea that a fish shock was really electrical ". . . seemed, in some respects, to combat the general principles of electricity" [2], as we will explain.

This experiment addressed the issue of the identity between the common type of electric fluid (e.g., the electricity produced by electrical friction machines and accumulated in capacitors such as Leyden jars) and the "fluid" involved in fish shock. Even though not published by Walsh, the news of his experiment spread to all the "Republic of Letters" (learned community) of the time, mainly owing to the wide circulation of Rozier's journal, and the description of the experiment in contemporary scientific publications (see, for example, [3]). Together with the news of Walsh's previous experiments on the torpedo, it promoted a fresh interest in the possible involvement of electricity in "animal economy" (animal physiology), and probably contributed to Luigi Galvani's decision to start his famous experiments on frog muscle contraction [4,5].

With time, however, memory of Walsh's experiment on the eel diminished gradually. Apparently, the experiment was unknown to Faraday, who repeated it in 1839 [6]. A few years before Faraday's experiment, Santi Linari and Carlo Matteucci succeeded in producing a spark from a torpedo [7,8] thus concluding the phase of research into electric fish started by Walsh in 1772. Memory of Walsh's experiment on the eel was lost, at least partially, to science historians also. For example, Mary Brazier cast doubts on Walsh's achievement. In referring to Walsh and to the spark, she writes that "later it was claimed that he had demonstrated this with the Gymnotus," and "a discourse on the history of the electric properties of the torpedo, delivered in 1775 to the Royal Society by the eminent Sir John Pringle, mentioned no sparks" [9]. However, the discourse of Pringle, printed in 1775, was delivered on November 30, 1774 upon awarding Walsh the Copley medal (a kind of Nobel prize for the time) for his previous studies on the torpedo, and, thus, preceded Walsh's achievement with the eel [10]. Walsh himself seems destined to oblivion, notwithstanding all the important work that he did on the torpedo and all the further research he promoted directly or indirectly. Walsh's name is not listed in the Dictionary of Scientific Biography, or in recent editions of the Encyclopedia Britannica.

Among the witnesses to Walsh's experiment on the eel, Le Roy mentions more than 40 fellows of the Royal Society, and, from their report, we know that the shock could pass through a chain of 27 persons (all feeling it) and the experiment "was repeated up to ten, twelve times." The crucial importance of the event is attested by the sudden "conversion" of William Henly, an eminent "electrician" of the time. Shortly before the experiment, Henly outlined his skepticism about the electric nature of fish shock in an expressive way.

When a Gentleman can so give up his reason as to believe in the possibility of an accumulation of electricity among conductors sufficient to produce the effects ascribed to the Torpedo, he need not hesitate a moment to embrace as truths the greatest contradictions that can be laid before him. [11]

However, after attending Walsh's experiment, he became enthusiastic and planned to determine the direction of the spark by using an apparatus built for this purpose [12]. Henly's original skepticism concerned the objections raised in the 18th century against the possibility that electricity could be accumulated in living tissues and involved in some physiological mechanisms and particularly in nervous conduction. This possibility was challenged by Albrecht von Haller and his followers. Electricity, they argued, tends to diffuse from where it is in excess to where there is less if the two places are connected by conductive substances [13]. Because living tissues conduct electricity, no stable imbalance could exist inside animal bodies, and, consequently, the force required to move electricity through nerves for their function would not be present. Furthermore, it was difficult to envision how electric flux could be restricted to the specific nerve paths required by physiological needs. Were the nervous fluid of an electrical nature, argued Haller, we would move all the muscles of the foot when we wanted to move a single toe [14]. In the case of fish, a further difficulty arose from the conductive nature of their natural habitat; an "electric fish" seemed a nonsense, somewhat like a charged Leyden jar plunged in water.

In spite of these difficulties, however, fish shock appeared to be similar to that produced by a Leyden jar (as noticed soon after the invention of this first electric capacitor). Moreover, it was transmitted by conductive bodies and arrested by insulating matters in a similar manner to the discharge of the Leyden jar. On the basis of such observations made on the "torporific" eel of Guiana, Edward Bancroft questioned the mechanical interpretation of the torpedo discharge advocated by René-Antoine De Réaumur.

. . .it is self-evident that, either the mechanisms and properties of the Torpedo and those of the Torporific Eel are widely different, or that Mons. De Réaumur has amused the world with an imaginary hypothesis: and, from my own observations, as well as the information which I have been able to obtain on this subject, I am disposed to embrace the latter inference. [15]

Encouraged by discussions with Benjamin Franklin, Walsh decided to verify Bancroft's assertion, and in 1772 he crossed the channel, convinced of the impossibility of obtaining live torpedoes in England (see, however, [16]). From June 26th to July 27th he carried out an extended series of experiments on torpedoes at La Rochelle and l'Isle de Ré that convinced him fully of the electrical nature of their discharge. These experiments were published in 1773 in the form of a letter to Benjamin Franklin, together with the anatomical observations performed by John Hunter on the same torpedoes used in physiological studies [2,17] (figure 2).

Walsh's investigations are reported also in a lively form in a "journal of experiments" manuscript, also neglected by historians, in which a description of the progress of daily work is presented, together with "reflections" and annotations of various natures [18]. Through these writings, we can follow, from a privileged point of view, a crucial phase of the scientific progress of the 18th century. The electric fish, for centuries an object of curiosities and legends, more suited for a Wunderkammer than for a laboratory [19,20], became the subject of a scientific investigation that, as Walsh anticipated, could open "a large field for interesting enquiry, both to the electrician in his walk of physics, and to all who consider, particularly or generally, the animal economy" [2]. This passage may be considered, a posteriori, somewhat "prophetic" if one considers that, through the work of Luigi Galvani, research on electric fish opened the path to modern electrophysiology [4,5] and, through the scientific endeavor of Alessandro Volta, led to the discovery of the laws of the capacitor and the invention of the electric battery [21] (figures 3,4).

As in the case of Galvani and Volta, Walsh's research was characterized by a productive interchange of a physical and physiological disposition. Upon his arrival at La Rochelle, and before obtaining live torpedoes, Walsh interrogated local fishermen and noted:

. . . gave one of them a small Shock with the Leyden Phial and repeated it; he insisted that the Effect was precisely the same with that of the Torpedo.

On June 30th, he experienced from "a female Torpedo" his first shock, which reached, he said, ". . . half way of the part of my arm above the Elbow; both instantaneous in commencement, and ending precisely as an Electric shock." A side-note testifies to Walsh's initial incredulity on the electrical nature of fish discharge.

On this my first experiment on the effect of the Torpedo, I exclaimed this certainly Electricity - but how?

On this point, however, Walsh passes rapidly from skepticism to enthusiasm. This occurred particularly on July 9th, during a long series of experiments in which Walsh and his nephew Arthur, forming a circuit with the fish, showed that the shock is transmitted by a metal, whereas it is arrested by glass and sealing wax. These experiments, varied and repeated many times, are reported in short notes that convey the idea of a rapid crescendo, as, for example, when comparing the conductive properties of different materials.

Touched the upper and lower sides of the same flank with Spoons; Shock, twice.
Repeated it with Spoons; a Shock.
With sealing Wax; nothing.
Repeated it with spoons; Six times.
With sealing wax, twice; nothing.

In the evening, Walsh announced publicly the electrical nature of the torpedo, and in his journal the pride of the discovery is manifested by a note in French - "Je l'ai donté" (i.e. "dompté," "I have tamed it"; figure 2) - alluding to a verse of the Latin poet Claudian, "Who did not hear of the untamed art of the wonderful Torpedo?" The announcement was made to eminent personalities of La Rochelle, some of whom, as members of the local Académie, were involved directly in these experiments. Three days later, Walsh sent a letter to Franklin (included in the 1773 paper), to communicate "with particular satisfaction . . . that the effect of the Torpedo is absolutely electrical," and asked him "to acquaint Dr. Bancroft of our having confirmed his suspicion concerning the torpedo."

During his last days at La Rochelle, Walsh gave public exhibitions of the "electric power of the Torpedo," which were reported in the Gazette de France, thanks to a correspondence of the Academy secretary and mayor of the town, Monsieur Seignette, who confirmed that the commotion experienced by various persons connected in a circle ". . . differed in nothing from that of the Leyden experiment" [2]. A later echo was the exhibition of the torpedo's shock requested of the Académie by the Austrian Emperor Joseph II, who, in 1775, experienced the shock personally [22].

However, in spite of similar characteristics between the torpedo's effects and artificial electricity, differences also "were remarked by the Company," who noticed that fish shock "was attended with neither Spark nor Sound, that it occasioned no Attraction and Repulsion." Before voltaic batteries, electricity was produced commonly with friction-type electric machines, thus, resulting in electric performances involving tiny charges and very high tensions (more that 10,000 V). Attraction and repulsion, sparks and sounds were, in these circumstances, landmarks of genuine electrical phenomena. Indeed, Walsh had tried, without success, to obtain these "typical" electrical signs from the torpedo with "a narrow strip of Tinfoil being pasted on a stick of sealing wax, and a very minute interstice made in the Tinfoil, by only drawing the edge of a sharp knife across it." A similar method was to be effective in 1775 with the eel, due to the larger potential of the shock of this fish (up to 600 V) compared with that of the torpedo (∼50 V).

Thus, torpedo electricity and genuine electricity did not appear to be identical. As for the absence of attraction and repulsion, Walsh could assume easily that the production of electricity by the fish was an instantaneous process, too rapid to produce any mechanical effect. It was more difficult to account for the absence of sparks and sounds, and for the inability of the shock to pass across "the minutest separation possible made in Tinfoil." These difficulties could not be dismissed by saying that torpedo electricity was weak. "The Torpedo" - Walsh notes - "often gives severe Shocks, his Electricity therefore cannot be deemed weak."

It is precisely in what seemed to be the most serious difficulties against the identity between "torpedinal" and electrical fluid, that the research started by Walsh proved to be of fundamental importance for the understanding of the physical laws involved in electric phenomena, as he had anticipated during his public exhibition at La Rochelle.

. . . as artificial Electricity had led to a discovery of some of the operations of the Animal, the Animal if well considered would lead to a discovery of some truths in artificial Electricity which were at present unknown and perhaps unsuspected.

As Walsh elaborated upon his return from France, the fish shock, with regard to both the "positive signs" of electrical nature (commotion and passage through conductive bodies) and "negative phenomena" (i.e., absence of attraction, repulsion, sparks, and sounds) "may be imitated by art" with purely physical devices [2]. Through a pneumatic analogy, Walsh assumed that electric effects do not depend exclusively on the quantity of electricity involved, but also on the "dense or rare state" that electric matter might assume. If a given quantity of electricity is "condensed," as it occurs in a "highly charged," "small Phial," then it will be "capable of forcing a passage through an inch of air, and afford the phenomena of light, sound, attraction, and repulsion." If the same quantity of electricity is made "rare" by communicating it to large Leyden jars, then "it will not now pass the hundredth part of that inch of air," and yet it could produce sensible effects. This last condition imitates the electrical state responsible for torpedo's shock, and Walsh mentions that "Mr. Cavendish" has, indeed, succeeded in showing "that a shock could be received from a charge which is unable to force the passage through the least space of air."

Here, Walsh alludes to the experiments that led Henry Cavendish to build up an "artificial torpedo" capable of imitating a natural torpedo, in producing strong shocks and lacking attraction, repulsion and visible sparks, and in the inability "to pass through the least sensible space of air." Like the natural fish, the artificial torpedo could also produce commotion even when immersed in water, if powered by many Leyden jars charged to a low degree. Cavendish gave public demonstrations of his device, and, in 1776, he published an important paper in which he identified the "degree of electrification" and the "quantity of electric fluid" as the determining factors responsible for electric effects. In some way, Cavendish anticipated Volta in the elaboration of the concepts of tension and charge and of the laws of the capacitor [23].

In his paper, Cavendish makes frequent allusions to Walsh's studies on the torpedo, and, in particular, he mentions that, according to him, the shock produced by many weakly charged Leyden jars resembles the shock of the natural torpedo more than that produced by a strongly charged small jar does. Both Walsh and Cavendish assumed that the torpedo could accommodate a great quantity of electric fluid, in an uncompressed state, in the large surface of the staked membranous elements that make up the structures denoted as "electric organs" by Walsh himself. At the end of the century, a reflection of the electric organs was to be of importance for Volta's invention of the electric battery. Volta would call it an "organe eléctrique artificiel," not only for its similar shape but also because, in his opinion, the battery resembled the natural organ in being capable of producing electricity by the "mere contact of conductive substances" [24] (figure 4).

The electric organs of fish were the subject of accurate anatomical studies by John Hunter (figure 5), whose association with Walsh and Cavendish in electric fish research seems to prefigure the interdisciplinary character of modern science. Hunter underlined the rich innervation of the electrical organs, supposing that it ". . . must on reflection appear as extraordinary as the phenomena they afford." With reference to the electrical nature of torpedo shock, Hunter supposed that nerves might be ". . . subservient to the formation, collection, or management of the electric fluid" and concluded, in a manner that appears to anticipate the importance of electric fish studies for the development of neurophysiology:

How far this may be connected with the power of the nerves in general, and how far it may lead to an explanation of their operations, times and future discoveries alone can fully determine. [17]

In spite of the evidence provided by Walsh and Cavendish, the apparent inability to draw a spark from the torpedo appeared to many as an expression of some essential difference between common electrical phenomena and fish shock. This explains the "crucial" importance that the scientists of those days attributed to Walsh's achievement with the eel, an importance commented on by Tiberio Cavallo in 1795 with these words:

The spark was considered the hallmark of electricity.

The subject of Animal Electricity was considerably advanced by the discovery of the spark, with which the shock of the Gymnotus was attended; for, notwithstanding the previous discoveries relating to the torpedo, and the actual possibility of imitating the effects of that animal's extraordinary power by means of a large battery weakly charged with artificial electricity, yet the scrupulous philosopher still suspected that the power of the torpedo might be something different from electricity, since the two principal characteristics of Electricity, namely the spark and attractions, had never been discovered in the torpedo. [25]

By demonstrating that electricity could serve a physiological process, the eel's spark undermined Haller's objections against the electrical nature of "nervous fluid." With regard to the principle responsible for neuromuscular functions, Felice Fontana, one of the strongest supporters of Haller's conceptions, wrote in 1781:

. . . that principle, if it be not common electricity, may be something, however, very analogous to it. The electrical Gymnotus and torpedo…make it at least possible, and this principle may be believed to follow the most common laws of electricity. [26]

In 1780, Galvani had indeed started the experiments that led him eventually to discover the existence of an intrinsic "animal electricity," analogous to that of electric fish, in the nerves and muscles of common animals (box 1; figure 3). At the time, Volta was interested also in electric fish research, and in 1782 he gave an account of Walsh's experiment, containing some noteworthy details based on a personal conversation with Walsh [27]. In particular, Volta wrote:

Mr. Walsh . . . has discovered in the said eel what can rightly be called an electric sense. If one puts in the water tub where the eel is, one, two, or more good conductors, but separated, the animal does not seem to be affected at all; but, as soon as a communication is established between two of these plunged conductors so as to complete the circuit, and the parts of the conductors that are outside the tub are also reunited, the animal becomes agitated, and rushes to them, and brings the extremity of its head to one end of this conductive arc as if he would like to smell it, he provokes the electric discharge, which hits the intermediate person or persons, assuming that these create the chain linking the two conductors.

Even this aspect of Walsh's work (mentioned also by other scientists of the time) has been largely ignored. In particular, it was unknown to those who tried to explain why some fish endowed with electric organs could avoid obstacles or localize prey in complete darkness. Possibly, this might explain why electroreception was discovered only about two centuries after Walsh [20].

Concluding Remarks

Buried in the dark side of scientific development, other important observations might be lost forever. The evolution of scientific knowledge from the past to the present might appear as sharp as the clear-cut profile of a bridge arch viewed from a distance. In Italo Calvino's Invisible Cities, Marco Polo remarks, however, that a bridge arch cannot exist without its constitutive stones [28]. John Walsh is one of the foundation stones of neurophysiology, and his scientific endeavor should be of interest, at least, to those who contribute now to the progress of this science.

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Endlinks

The Bicentennial of the Voltaic Battery (1800-2000): The Artificial Electric Organ - offers a new perspective on Volta's experiments, which led him to anticipate some important ideas that marked the inception of modern neuroscience. Fom Trends in Neurosciences, 2000, 23:4:147-151. Full text available from BioMedNet.

Electrophorus Electricus as a Model System for the Study of Membrane Excitability - examines the basic mechanisms involved in the generation of the electrical discharge of the electric eel and the membrane proteins involved. From Comparative Biochemistry and Physiology - Part A: Molecular and Integrative Physiology, 1998, 119:1:225-241.

Neuroscience History - lists the important events in the history of neuroscience research.

Milestones in Neuroscience Research - a collection of references that document the history of the neurosciences.

Historical Background - offers an overview of the history of 17th century neurophysiology. From The Brain Project.

International Society for the History of Neurosciences - offers a journal, news, a forum, and resources.

Neuroscience History Archives - a repository for information on American neuroscience in the twentieth century.

Neuroscience Timeline - although the timeline does not include Walsh, other important historical figures are highlighted.

Neurosciences on the Internet - a comprehensive, searchable index of neuroscience resources.

World Wide Web Virtual Library: Neuroscience - an alphabetical list of neuroscience resources, including many academic departments.

Related HMS Beagle article:

• The Eel - Fiction by Anna Tambour.

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